The most basic protection you can get is a battery-operated air pump which kicks in when the juice goes out:
http://www.jlaquatics.com/phpstore/s...ct_ID=px-apb11
There are also battery backup systems you can get from Canadian Tire designed to run things such as fridges and other appliances during blackouts which should keep a powerhead and heater going for a good while.
It also depends on the time of year and how well insulated the room is to prevent a temperature drop/rise.
A generator is the best, but there are other less-pricier options.